Osmotic and ionic regulation in different populations of the new zealand freshwater crayfish Paranephrops zealandicus

1. Some features of the osmoregulatory mechanism are compared in four populations of Paranephrops zeal andicus White collected form freshwaters of different ionic concentrations. 2. Crayfish from freshwaters of ca, 2-0 mM-NaCl concentration show a sustained decrease in blood concentration of ca. 8% when placed in 0-2 mM-NaCl. 3. Populations from freshwaters of ca. 0-2-0-4 mM-NaCl show lower rates of net salt loss in distilled water and higher rates of net salt uptake form dilute NaCl solutions than do populations from freshwaters of ca. 0-8-2-0 mM-NaCl. 4. Renal salt losses over the first 24 h in distilled water account for ca. 18% of the total salt loss. 5. It is suggested that P. zealandicus from environments of lowest concentration shows a similar degree of adaptation to freshwater as do crayfish of the northern hemisphere. It differs in possessing a substantially higher blood concentration.     

The bathtub does not hold water any more

This is the first part of a three part article under the general heading of ‘Off the bathtub onto the roller-coaster curve’, a short version¹ of which was presented at the 1988 Annual Reliability and Maintainability Symposium in U.S.A. The other two parts, to be published in later issues of this journal, are entitled ‘The roller-coaster curve is in’ and ‘Physical basis for the roller-coaster hazard rate curve’. This three-part article provides detailed discussions of the findings leading to the conclusions on the roller-coaster characteristics for the hazard rate curve for electronics. Part 1 being presented here covers the discussions on problems with the bathtub curve. The problems include making erroneous decisions resulting in reliability demonstration risks against the manufacturers, windfall profits for satellite manufacturers, false claims in reliability growth and reliability prediction accuracy and stress screening shortfalls. More important than the erroneous short-term decisions is the long-term reliability engineering methodology development. It is critical that we must reshape the course of reliability methodology development away from the bathtub misconception.     

Teams, signaling, and information theory

The purpose of this paper is to unify results from three separate and, at least superficially, unrelated subject matters, namely, team decision theory, market signaling in economics, and the classical Shannon information theory.     

Performance analysis of locking and optimistic concurrency control algorithms

New analytic models are presented which predict the maximum throughput of locking and optimistic concurrency control algorithms for a centralized database system. By making several simplifying assumptions, these models can be easily solved. The analytic results are tested against simulation and are shown to have an accuracy considerably better than some previously reported methods. The models are used to carry out a comparison between locking and optimistic control under stated assumptions. It is found that locking schemes consistently have higher maximum throughput than optimistic schemes.     

An Algorithm for Volume Estimation Based on Polyhedral Approxi mation

A volume algorithm is established which uses the data generated by computed tomography (CT) or ultrasound scans. The algorithm is based on a polyhedral reconstruction of an object of interest. Phantom studies indicate that the algorithm calculated volume is accurate within 3 percent. In a controlled clinical experiment on a laboratory animal, the algorithm calculated volume showed a maximum error of about 5 percent. In less controllable applications to human clinical data, volume calculations showed variations ranging up to 16 percent.